Method and apparatus for manufacturing semi-solid metallic slurry

ABSTRACT

The present invention provides a method and apparatus for manufacturing a high-quality semi-solid metallic slurry containing fine, uniform spherical particles that can be readily and conveniently applied to a subsequent process, with improvements in energy efficiency and mechanical properties, cost reduction, convenience of casting, and shorter manufacturing time. The semi-solid metallic slurry manufacturing method includes applying an electromagnetic field to a space containing a slurry vessel, loading a molten metal into the slurry vessel in a state where the electromagnetic field is applied to the space, and drawing the slurry vessel out from the space. The semi-solid metallic slurry manufacturing apparatus includes at least one slurry vessel, at least one stirring unit having a space for the at least one slurry vessel and applying an electromagnetic field to the space, a driving unit moving the slurry vessel at least up and down to place the slurry vessel in the space, and a loading unit loading a molten metal in liquid state into the slurry vessel.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority from Korean Patent ApplicationNos. 2002-58163 filed on Sep. 25, 2002; 2002-63162 filed on Oct. 16,2002; 2003-3250 filed on Jan. 17, 2003; and 2003-13517 filed on Mar. 4,2003, the disclosures of which are incorporated herein in their entiretyby reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a method and apparatus formanufacturing a semi-solid metallic slurry, and more particularly, to amethod and apparatus for manufacturing a semi-solid metallic slurry, ina solid and liquid combined state, containing fine, uniform sphericalparticles.

[0004] 2. Description of the Related Art

[0005] Semi-solid metallic slurries refer to metallic materials in asolid and liquid combined phase for use in a rheocasting orthioxocasting process. Semi-solid metallic slurries consist of sphericalsolid particles suspended in a liquid phase in an appropriate ratio attemperature ranges for semi-solid state, and thus, they change formeasily by a small force due to their thioxotropic properties and can becast easily like a liquid due to their high fluidity. Rheocasting refersto a process of manufacturing billets or mold products from metallicslurries having a predetermined viscosity through casting or forging.Thixocasting refers to a process involving reheating billetsmanufactured through rheocasting back into a metal slurry and casting orforging the metal slurry to manufacture final products.

[0006] Such rheocasting orthixocasting is more advantageous than generalforming processes, such as casting or forging, using molten metal. Forexample, semi-solid or semi-molten slurries used in rheocasting orthixocasting have fluidity at a lower temperature than molten metal, sothat the die casting temperature can be lowered in rheocasting orthixocasting, thereby ensuring an extended lifespan of the die. Inaddition, when a semi-solid or semi-molten metallic slurry is extrudedthrough a cylinder, turbulence is less likely to occur, and less air isincorporated during casting, thereby preventing formation of air pocketsin final products. Besides, the use of semi-solid or semi-moltenmetallic slurries leads to reduced shrinkage during solidification,improved working efficiency, mechanical properties, and anti-corrosion,and lightweight products. Therefore, such semi-solid or semi-moltenmetallic slurries can be used as new materials in the fields ofautomobiles, airplanes, and electrical, electronic informationcommunications equipment.

[0007] As described above, semi-solid slurries solidified from moltenmetal by a predetermined method are used in rheocasting, and semi-moltenslurries obtained by reheating solid billets are used in thixocasting.Throughout the specification of the present invention, the term“semi-solid metallic slurry” means a metallic slurry in a solid andliquid combined stage at a temperature range, between the liquidustemperature and the solidus temperature of the metal, which can bemanufactured by rheocasting through solidification of molten metal.

[0008] In conventional rheocasting, molten metal is stirred at atemperature of lower than the liquidus temperature while cooling, tobreak up dendritic structures into spherical particles suitable forrheocasting, for example, by mechanical stirring, electromagneticstirring, gas bubbling, low-frequency, high-frequency, orelectromagnetic wave vibration, electrical shock agitation, etc.

[0009] As an example, U.S. Pat. No. 3,948,650 discloses a method andapparatus for manufacturing a liquid-solid mixture. In this method,molten metal is vigorously stirred while cooled to be solidified. Asemi-solid metallic slurry manufacturing apparatus disclosed in thispatent uses a stirrer to induce flow of the solid-liquid mixture havinga predetermined viscosity to break up dendritic crystalline structuresor disperse broken dendritic crystalline structures in the liquid-solidmixture. In this method, dendritic crystalline structures formed duringcooling are broken up and used as nuclei for spherical particles.However, due to generation of latent heat of solidification at the earlystage of cooling, the method causes problems of low cooling rate,manufacturing time increase, uneven temperature distribution in a mixingvessel, and non-uniform crystalline structure. Mechanical stirringapplied in the semi-solid metallic slurry manufacturing apparatusinherently leads to non-uniform temperature distribution in the mixingvessel. In addition, the apparatus is operated in a chamber, therebymaking it difficult to continuously perform a subsequent process.

[0010] U.S. Pat. No. 4,465,118 discloses a method and apparatus formanufacturing a semi-solid alloy slurry. This apparatus includes acoiled electromagnetic field application unit, a cooling manifold, and avessel, which are sequentially formed inward, wherein molten metal iscontinuously loaded down into the vessel, and cooling water is flowedthrough the cooling manifold to cool the outer wall of the vessel. Inmanufacturing a semi-solid alloy slurry, molten metal is injectedthrough a top opening of the vessel and cooled by the cooling manifold,thereby resulting in a solidification zone in the vessel. Cooling issustained while a magnetic field is applied by the electromagnetic fieldapplication unit to break up dendritic crystalline structures formed inthe solidification zone and to pull an ingot from the slurry through thelower end of the apparatus. The basic technical idea of this method andapparatus is to break up dendritic crystalline structures aftersolidification by applying vibration. However, many problems, such ascomplicated processing and non-uniform particle structure, arise withthis method. In the manufacturing apparatus, since molten metal iscontinuously supplied to grow an ingot, it is difficult to control thestate of the metal ingot and the overall process. Moreover, the vesselis cooled using water prior to applying an electromagnetic field, sothat there is a great temperature difference between the peripheral andcore regions of the vessel.

[0011] Other types of rheocasting and thixocasting described later areavailable. However, all of the methods are based on the technical ideaof breaking up dendritic crystalline structures after formation, togenerate nuclei of spherical particles, and arise such problemsdescribed in conjunction with the above patents.

[0012] U.S. Pat. No. 4,694,881 discloses a method for manufacturingthixotropic materials. In this method, an alloy is heated to atemperature at which all metallic components of the alloy are present ina liquid phase, and the resulting molten metal is cooled to atemperature between its liquidus and solidus temperatures. Then, themolten metal is subjected to a sufficient shearing force to breakdendritic structures formed during the cooling of the molten metal, sothat thixotropic materials are manufactured.

[0013] Japanese Patent Laid-open Application No. 11-33692 discloses amethod for producing a metallic slurry for rheocasting. In this method,a molten metal is supplied into a vessel at a temperature near itsliquidus temperature or 50° C. above its liquidus temperature. Next,when at least a portion of the molten metal reaches a temperature lowerthan the liquidus temperature, i.e., the molten metal is cooled below aliquidus temperature range, the molten metal is subjected to a force,for example, ultrasonic vibration. Finally, the molten metal is slowlycooled into a metallic slurry for rheocasting containing sphericalparticles. This method also uses a physical force, such as ultrasonicvibration, to break up the dendrites grown at the early stage ofsolidification. In this method, if the casting temperature is greaterthan the liquidus temperature, it is difficult to form sphericalparticle structures and to rapidly cool the molten metal. Furthermore,this method leads to a non-uniformity of surface and core structures.

[0014] Japanese Patent Laid-open Application No. 10-128516 discloses acasting method of thixotropic metal. This method involves loading amolten metal into a vessel and vibrating the molten metal using avibrating bar dipped in the molten metal to directly transfer itsvibrating force to the molten metal. A molten alloy containing nuclei,which is a semi-solid and semi-liquid state, at temperatures lower thanits liquidus temperature is formed and cooled to a temperature at whichit has a predetermined liquid fraction and held from 30 seconds to 60minutes to allow nuclei in the molten alloy to grow larger, therebyresulting in thixotropic metal. This method provides relatively largeparticles of about 100 μm and takes a considerably long processing time,and cannot be performed in a larger vessel than a predetermined size.

[0015] U.S. Pat. No. 6,432,160 B1 discloses a method for making athixotropic metal slurry. This method involves simultaneouslycontrolling the cooling and the stirring of molten metal to form athixotropic metal slurry. In particular, after loading a molten metalinto a mixing vessel, a stator assembly positioned around the mixingvessel is operated to generate a magnetomotive force sufficient to stirthe molten metal in the vessel rapidly. Next, the temperature of themolten metal is rapidly dropped by means of a thermal jacket equippedaround the mixing vessel for precise control of the temperature of themixing vessel and the molten metal. The molten metal is continuouslystirred during cooling cycle in a controlled manner. When the solidfraction of the molten metal is low, high stirring rate is provided. Asthe solid fraction increases, a greater magnetomotive force is applied.

[0016] Most of the above-described conventional methods and apparatusesfor manufacturing semi-solid metal slurries use shear force to breakdendritic structures into spherical structures during a cooling process.Since a force such as vibration is applied after the temperature of atleast a portion of the molten metal drops below its liquidustemperature, latent heat is generated due to the formation of initialsolidification layers. As a result, there are many disadvantages such asreduced cooling rate and increased manufacturing time. In addition, dueto a non-uniform temperature between the inner wall and the center ofthe vessel, it is difficult to form fine, uniform spherical metalparticles. This structural non-uniformity of metal particles will begreater if the temperature of the molten metal loaded into the vessel isnot controlled.

SUMMARY OF THE INVENTION

[0017] The present invention provides a method and apparatus formanufacturing a semi-solid metallic slurry containing fine, uniformspherical particles, with improvements in energy efficiency andmechanical properties, cost reduction, convenience of casting, andshorter manufacturing time.

[0018] The present invention also provides a method and apparatus formanufacturing a high-quality semi-solid metallic slurry within a shorttime, which can be readily and conveniently applied to a subsequentprocess.

[0019] In accordance with an aspect of the present invention, there isprovided a method for manufacturing a semi-solid metallic slurry, themethod comprising applying an electromagnetic field to a spacecontaining a slurry vessel; loading a molten metal into the slurryvessel in a state where the electromagnetic field is applied to thespace; and drawing the slurry vessel out from the space.

[0020] According to a specific embodiment of the semi-solid metallicslurry manufacturing method, applying the electromagnetic field to thespace is performed prior to loading the molten metal into the slurryvessel. In this case, the slurry vessel is placed in the space afterapplying the electromagnetic field to the space.

[0021] Further, applying the electromagnetic field to the space may beperformed at the start of loading the molten metal into the slurryvessel. Alternatively, applying the electromagnetic field to the spacemay be performed in the middle of loading the molten metal into theslurry vessel.

[0022] Further, applying the electromagnetic field to the space may besustained until a slurry in the slurry vessel has a solid fraction of0.001-0.7, preferably, 0.001-0.4, more preferably, 0.001-0.1.

[0023] The method for manufacturing a semi-solid metallic slurry mayfurther comprising cooling the slurry vessel containing the molten metalafter loading the molten metal into the slurry vessel. In this case,cooling the slurry vessel containing the molten metal is sustained untila slurry in the slurry vessel has a solid fraction of approximately0.1-0.7. Cooling the slurry vessel containing the molten metal may beperformed at a rate of 0.2-5.0° C./sec, preferably, 0.2-2.0° C./sec.

[0024] In accordance with another aspect of the present invention, thereis provided an apparatus for manufacturing a semi-solid metallic slurry,the apparatus comprises at least one slurry vessel; at least onestirring unit having a space for the at least one slurry vessel andapplying an electromagnetic field to the space; a driving unit movingthe slurry vessel at least up and down to place the slurry vessel in thespace; and a loading unit loading a molten metal in liquid state intothe slurry vessel.

[0025] According to specific embodiments of the semi-solid metallicslurry manufacturing apparatus, the at least one stirring unit appliesthe electromagnetic field to the space prior to loading the molten metalinto the at least one slurry vessel. The at least one stirring unitapplies the electromagnetic field to the space at the start of loadingthe molten metal into the at least one slurry vessel. The at least onestirring unit applies the electromagnetic field to the space in themiddle of loading the molten metal into the at least one slurry vessel.

[0026] Further, the driving unit may move the slurry vessel up after apredetermined time from loading the molten metal into the at least oneslurry vessel to draw the at least one slurry vessel out from the space.

[0027] Further, the driving unit may laterally shift the at least oneslurry vessel. In this case, the driving unit may comprise a rotaryplate supporting the at least one slurry vessel at an edge. The drivingunit with the rotary plate moves the at least one slurry vessel downafter a predetermined time from loading the molten metal into the atleast one slurry vessel, and rotates the rotary plate to draw the atleast one slurry vessel out from the space.

[0028] Further, the driving unit may be constructed to be laterallymoveable along a rail, so that it moves the at least one slurry vesseldown after a predetermined from loading the molten metal into the atleast one slurry vessel, and is moved along the rail to draw the atleast one slurry vessel out from the space.

[0029] According to a specific embodiment of the semi-solid metallicslurry manufacturing apparatus, the at least one stirring unit appliesthe electromagnetic field to the space until a slurry in the at leastone slurry vessel has a solid fraction of approximately 0.001-0.7,preferably, 0.001-0.4, more preferably, 0.001-0.1.

[0030] In specific embodiments, the at least one slurry vessel used inthe semi-solid metallic slurry manufacturing apparatus may include atemperature control element. This temperature control element maycomprise at least one of a cooler installed in the at least one slurryvessel and an external electric heater. The temperature control elementcools a slurry in the at least one slurry vessel to reach a solidfraction of approximately 0.1-0.7. The temperature control element coolsa slurry in the at least one slurry vessel at a rate of approximately0.2-5.0° C./sec, preferably, 0.2-2.0° C./sec.

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The above and other features and advantages of the presentinvention will become more apparent by describing in detail exemplaryembodiments thereof with reference to the attached drawings in which:

[0032]FIG. 1 is a graph of temperature profile applied in a method formanufacturing a semi-solid metallic slurry according to the presentinvention;

[0033]FIGS. 2 and 3 illustrate a structure of an apparatus formanufacturing a semi-solid metallic slurry according to an exemplaryembodiment of the present invention;

[0034]FIG. 4 is a sectional view of an example of a slurry vessel usedin a semi-solid metallic slurry manufacturing apparatus according to thepresent invention;

[0035]FIG. 5 illustrates a structure of a semi-solid metallic slurrymanufacturing apparatus according to another exemplary embodiment of thepresent invention;

[0036]FIG. 6 illustrates a structure of a semi-solid metallic slurrymanufacturing apparatus according to still another exemplary embodimentof the present invention;

[0037] FIGS. 7(a)-(e) illustrate the operation of the semi-solidmetallic slurry manufacturing apparatus of FIG. 6; and

[0038]FIG. 8 illustrates a structure of a semi-solid metallic slurrymanufacturing apparatus according to yet still another exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0039] The present invention will be described more fully in thefollowing exemplary embodiments of the invention with reference to theaccompanying drawings.

[0040] Unlike the above-described conventional techniques, a method ofmanufacturing a semi-solid metallic slurry according to the presentinvention includes stirring molten metal by applying an electromagneticfield prior to the completion of loading the molten metal into a vessel.In other words, electromagnetic stirring is performed prior to or at thestart or in the middle of loading the molten metal into the vessel, toprevent formation of dendritric structures. Ultrasonic waves instead ofthe electromagnetic field can be applied for stirring.

[0041] In particular, an empty vessel is positioned in a space of asemi-solid metallic slurry manufacturing apparatus. An electromagneticfield is applied to the space, and molten metal is loaded into thevessel. The intensity of the applied electromagnetic field is strongenough to stir the molten metal.

[0042]FIG. 1 is a graph of temperature profile applied in a method formanufacturing a semi-solid metallic slurry according to the presentinvention. As shown in FIG. 1, molten metal is loaded into the vessel ata temperature Tp. As described above, an electromagnetic field may beapplied to the vessel prior to loading molten metal into the vessel.Alternatively, the vessel may be positioned in the space after theapplication of an electromagnetic field into the space. However, thepresent invention is not limited to this, and electromagnetic stirringmay be performed at the start or in the middle of loading the moltenmetal into the vessel.

[0043] Due to the electromagnetic stirring performed prior to thecompletion of loading molten metal into the vessel, the molten metaldoes not form dendritic structures near the inner wall of the vessel atthe early stage of solidification, and numerous micronuclei areconcurrently generated throughout the vessel because the temperature ofthe entire molten metal is rapidly dropped to a temperature lower thanits liquidus temperature.

[0044] Applying an electromagnetic field to the vessel prior orsimultaneously to loading molten metal into the vessel leads to activestirring of the molten metal in the center and the inner wall regions ofthe vessel and rapid heat transfer throughout the vessel, therebysuppressing the formation of solidification layers near the inner wallof the vessel at the early stage of cooling. In addition, such activestirring of the molten metal induces smooth convection heat transferbetween the higher temperature molten metal and the lower temperatureinner vessel wall, so that the molten metal can be cooled rapidly. Dueto the electromagnetic stirring, particles contained in the molten metalscatter upon loading into the vessel and are dispersed throughout thevessel as nuclei, so that a temperature difference in the vessel hardlyoccurs during cooling. However, in conventional techniques where moltenmetal is stirred after the completion of loading into a vessel, thetemperature of the molten metal suddenly drops as soon as it contactsthe low temperature inner vessel wall, so that dendritic crystals growfrom solidification layers formed near the inner wall of the vessel atthe early stage of cooling.

[0045] The principles of the present invention will become more apparentwhen described in connection with latent heat of solidification. In amethod for manufacturing a semi-solid metallic slurry according to thepresent invention, molten metal does not solidify near the inner vesselwall at the early stage of cooling, and no latent heat of solidificationis generated. Accordingly, the amount of heat to be dissipated from themolten metal for cooling is equivalent only to the specific heat of themolten metal that corresponds to about {fraction (1/400)} of the latentheat of solidification. Therefore, dendrites, which are generatedfrequently when using conventional methods near the inner vessel wall atthe early stage of cooling, are not formed, and the entire molten metalin the vessel can be uniformly cooled. It takes merely about 1-10seconds from the loading of the molten metal. As a result, numerousnuclei are created and dispersed uniformly throughout the entire moltenmetal in the vessel. The increased density of nuclei shortens thedistance between the nuclei, and spherical particles instead ofdendritic particles are grown.

[0046] The same effects can be achieved even when an electromagneticfield is applied in the middle of loading the molten metal into thevessel. In other words, solidification layers are hardly formed near theinner vessel wall even when electromagnetic stirring begins in themiddle of loading the molten metal into the vessel.

[0047] It is preferable that the temperature, Tp, of the molten metal bemaintained in a range from its liquidus temperature to 100° C. above theliquidus temperature (melt superheat=0˜100° C.) at the time of beingloaded into the vessel. According to the present invention, since theentire vessel containing the molten metal is cooled uniformly, it allowsfor the loading of the molten metal into the vessel at a temperature of100° C. above its liquidus temperature, without the need to cool thetemperature of the molten metal to near its liquidus temperature.

[0048] On the other hand, in conventional methods, an electromagneticfield is applied to a vessel after the completion of loading moltenmetal into a vessel and a portion of the molten metal reaches below itsliquidus temperature. Accordingly, latent heat is generated due to theformation of solidification layers near the inner wall of the vessel atthe early stage of cooling. Because the latent heat of solidification isabout 400 times greater than the specific heat of the molten metal, ittakes much time to drop the temperature of the entire molten metal belowits liquidus temperature. Therefore, in these conventional methods, themolten metal is loaded into the vessel after the molten metal has cooledto a temperature near its liquidus temperature or to a temperature of50° C. above its liquidus temperature.

[0049] According to the present invention, the electromagnetic stirringmay be stopped at any point after at least a portion of the molten metalin the vessel reaches a temperature lower than its liquidus temperatureT₁, i.e., after nuclei are created in the molten metal at a solidfraction of about 0.001, as illustrated in FIG. 1. For example, anelectromagnetic field may be applied to the molten metal in the vesselthroughout all the cooling process of the molten metal, but prior to asubsequent forming process such as die casting or hot forging. This isbecause, once nuclei are distributed uniformly throughout the vessel,the electromagnetic stirring does not affect the growth of crystallineparticles from the nuclei in the metallic slurry. Therefore, theelectromagnetic stirring can be sustained until the solid fraction ofthe molten metal reaches at least 0.001-0.7. However, theelectromagnetic stirring is sustained until the solid fraction of themolten metal reaches the range of, preferably, 0.001-0.4, and morepreferably, 0.001-0.1, for energy efficiency.

[0050] After the electromagnetic stirring is completed, the vesselcontaining the metallic slurry is drawn out from the electromagneticfield application space for a continuous subsequent process, forexample, die casting, hot forging, billet formation. The vesselcontaining the metallic slurry may be drawn out from the electromagneticfield application space irrespective of the termination of theelectromagnetic stirring, i.e., after or during the application of theelectromagnetic field.

[0051] According to the present invention, the application of anelectromagnetic field performed prior to the completion of loading themolten metal into the vessel to form and uniformly distribute nuclei inthe molten metal is followed by cooling to facilitate the growth of thenuclei. This cooling process may be performed simultaneously to loadingthe molten metal into the vessel.

[0052] As described above, the application of the electromagnetic fieldmay be sustained throughout all the cooling process. In other worlds,cooling may be performed when the vessel containing the metallic slurrystays in the electromagnetic field application space, i.e., prior to thevessel being drawn out from the electromagnetic field application space.As a result, a semi-solid metallic slurry is manufactured in theelectromagnetic field application space and readily subjected to afollowing forming process.

[0053] The cooling process may be sustained just prior to a subsequentforming process, preferably, until the solid fraction of the moltenmetal reaches approximately 0.1-0.7, i.e., up to time t₂ of FIG. 1. Themolten metal may be cooled at a rate of approximately 0.2-5.0° C./sec,preferably, 0.2-2.0° C./sec depending on a desired distribution ofnuclei and a desired size of particles.

[0054] A semi-solid metallic slurry containing a predetermined amount ofsolid is manufactured through the above-described processes and readilysubjected to billet formation, by rapid cooling, for thixocasting or diecasting, forging, or pressing to form final products.

[0055] According to the present invention described above, a semi-solidmetallic slurry can be manufactured within a short time, merely in 30-60seconds from loading the molten metal into the vessel for a metallicslurry with a solid fraction of approximately 0.1-0.7. In addition,formed products having a uniform, dense spherical crystalline structurecan be manufactured from the semi-solid metallic slurry formed by themethod according to the present invention.

[0056] The above-described method for manufacturing a semi-solidmetallic slurry according to the present invention can be performedusing an apparatus according to an embodiment of the present inventionillustrated in FIGS. 2 and 3.

[0057] Referring to FIG. 2, a semi-solid metallic slurry manufacturingapparatus according to an embodiment of the present invention includes aspace 13 to which an electromagnetic field is applied, a stirring unit 1equipped with a coil 11 for applying an electromagnetic field tosurround the space 13, at least one slurry vessel 2 that can beaccommodated in the space 13, a driving unit 3 for moving the slurryvessel 2 at least up and down, a loading unit 4 via which molten metalis loaded into the slurry vessel 2, and a controller 5.

[0058] The stirring unit 1 is mounted on the top of a base plate 14having a hollow member 14 a. The base plate 14 is installed at apredetermined height from the ground while supported by a support member15. The coil 11 for applying an electromagnetic field is mounted on thebase plate 14 around the hollow member 14 a, while supported by a frame12 having an inner space for the space 13. The coil 11 is electricallyconnected to the controller 5 and applies a predetermined intensity ofelectromagnetic field to the space 13 to electromagnetically stir themolten metal contained in the slurry vessel 2 placed in the space 13.Although not illustrated in FIG. 2, the stirring unit 1 may beimplemented as an ultrasonic stirrer.

[0059] The slurry vessel 2 may be formed of a metallic material or aninsulating material and may have any size and any shape that can beaccommodated in the space 13 surrounded by the stirring unit 1. However,it is preferable that the slurry vessel 2 is formed of a material havinga higher melting point than the molten metal to be loaded thereinto. Theslurry vessel 2 may have a lower stepped portion 21 that fits a vesselreceiver 33, to be described later, to lock the slurry vessel 2 into thespace 13. Although not illustrated in FIG. 2, a thermocouple may beinstalled in the slurry vessel 2 and connected to the controller 5 toprovide temperature information on the slurry vessel 2 to the controller5.

[0060] The slurry vessel 2 may be formed with a simple structure forcontaining molten metal, as illustrated in FIGS. 2 and 3. However, theslurry vessel 2 may further comprise a temperature control element 20,as illustrated in FIG. 4. The temperature control element 20 iscomprised of a cooler and/or a heater. In the embodiment of FIG. 4, acooling water pipe 23 is embedded in a vessel body 22. Although notillustrated, alternatively, an electric heater with a heating coil maybe further installed outside the slurry vessel 2. In addition, thecooler may be implemented as a water jacket additionally attachedoutside the slurry vessel 2, instead of the cooling water pipe 23. Thecooler, the heater, or a combination of the two may be installed in theslurry vessel 2 to cool the molten metal contained in the slurry vessel2 at an appropriate rate. It will be obvious that such a slurry vessel 2can be applied to all of the following embodiments of a semi-solidmetallic slurry manufacturing apparatus according to the presentinvention.

[0061] The driving unit 3 moves the slurry vessel 2 to place it in thespace 13 and to draw it out from the space 13. The driving unit 3 isimplemented with a driving motor and a gear or a hydraulic cylinder,etc. For example, the driving unit 3 may comprise a power system 31electrically connected to the controller 5, a piston 32 connected to andactuated by the power system 31 to move up and down in the space 13, anda vessel receiver 33 attached to an end of the piston 32 near the space13 to support the slurry vessel 2 therein. The slurry vessel 2 is placedin the space 13 to fit the vessel receiver 33.

[0062] In a state where the driving unit 3 is operated to raise thepiston 32 to place the slurry vessel 2 in the space 13, the loading unit4 supplies a molten metal in liquid state into the slurry vessel 2. Theloading unit 4 may be implemented with a general ladle, which iselectrically connected to the controller 5. Any device for loadingmolten metal into the slurry vessel 2 can be used for the loading unit4.

[0063] In the embodiment of a semi-solid metallic slurry manufacturingapparatus according to the present invention illustrated in FIG. 2,after the driving unit 3 is operated to place the slurry vessel 2 in thespace 13, an electromagnetic field having a predetermined frequency isapplied to the space 13 at a predetermined intensity by the coil 11 ofthe stirring unit 1. Alternatively, the slurry vessel 2 may be placed inthe space 13 after the application of the electromagnetic field to thespace 13. Next, a metal molten in a separate electrical furnace isloaded via the loading unit 4 into the slurry vessel 2 under theelectromagnetic field. Applying an electromagnetic field to the space 13may be performed at the start or in the middle of loading molten metalinto the vessel 2, in addition to prior to the loading, as describedabove.

[0064] After a predetermined period of time from the loading of themolten metal into the slurry vessel 2, the driving unit 3 is operated toraise the slurry vessel 2, as illustrated in FIG. 3, to draw the slurryvessel 2 out from the space 13 and to load another empty vessel into thespace 13, for example, using a transfer unit such as a robot. Next, theslurry vessel 2 drawn out from the space 13 is subjected to cooling at apredetermined rate until the solid fraction of a resulting semi-solidmetallic slurry reaches the range of 0.1-0.7. The molten metal in theslurry vessel 2 may be cooled at a rate of approximately 0.2-5.0°C./sec, preferably, 0.2-2.0° C./sec. Alternatively, the molten metal inthe slurry vessel 2 may be cooled prior to being drawn out from thespace 13 by the driving unit 3. In this case, after the completion ofcooling the molten metal in the slurry vessel 2, the slurry vessel 2 isdrawn out from the space 13 and replaced with another empty vessel.

[0065] The application of an electromagnetic field to the space 13 maybe sustained throughout all the cooling process, i.e., prior to drawingthe slurry vessel 2 out from the space 13 by the operation of thedriving unit 3, until the solid fraction of the resulting semi-solidmetallic slurry reaches the range of approximately 0.001-0.7. However,the application of an electromagnetic field to the space 13 by the coil11 is sustained after loading the molten metal into the slurry vessel 2until the solid fraction reaches, preferably, at least 0.001-0.4, morepreferably, 0.001-0.1, for energy efficiency, as described above. Thetime required for the solid fraction to reach such a level can beexperimentally measured. It is obvious that cooling can be performedwhile the electromagnetic field is applied to the space 13, as describedabove.

[0066] As illustrated in FIG. 5, a semi-solid metallic slurrymanufacturing apparatus according to another embodiment of the presentinvention includes at least two slurry vessels 2 a and 2 b forsimultaneous slurry formations. The basic structure of the semi-solidmetallic slurry manufacturing apparatus in this embodiment is the sameas in the previous embodiment, and thus, a detailed description thereonwill be omitted here. In the embodiment of FIG. 5, two vessel receivers33 a and 33 b for the at least two slurry vessels 2 a and 2 b aremounted on a receiver plate 34. It is preferable that the height of thevessel receivers 33 a and 33 b is substantially equal to the height ofthe spaces 13 a and 13 b such that the slurry vessels 2 a and 2 b fittedinto the vessel receivers 33 a and 33 b can be raised up to the top ofthe spaces 13 a and 13 b to be drawn out therefrom, respectively.

[0067]FIG. 6 illustrates a semi-solid metallic slurry manufacturingapparatus according to still another embodiment of the presentinvention, which differs from the previous embodiments in that thedriving unit 3 is constructed to be able to laterally shift the slurryvessel 2. The following description will be focused on this differencefrom the previous embodiments.

[0068] Referring to FIG. 6, a semi-solid metallic slurry manufacturingapparatus according to still another embodiment of the present inventionincludes a rotary plate 35 attached to an end of the piston 32 of thedriving unit 3. The piston 32 is attached to nearly the center of therotary plate 35. At least two vessel receivers 33 a and 33 b are mountedat the edge of the rotary plate 35, and the slurry vessels 2 a and 2 bare fitted into the vessel receivers 33 a and 33 b, respectively. Thepower system 31 is constructed to be able to move up and down and rotatethe piston 32. As the rotary plate 35 is rotated by the power system 31,the slurry vessel 2 a is laterally shifted away from the space 13, asshown in FIG. 6. The operation of the semi-solid metallic slurrymanufacturing apparatus of FIG. 6 will be described detail withreference to FIG. 7.

[0069]FIG. 7 sequentially illustrates the operation of the semi-solidmetallic slurry manufacturing apparatus of FIG. 6. As illustrated inFIG. 7(a), the piston 32 is raised to place the first slurry vessel 2 ain the space 13, and an electromagnetic field is applied to the space 13by the coil 11 of the stirring unit 1. Alternatively, the first slurryvessel 2 a may be placed in the space 13 after the application of anelectromagnetic field.

[0070] Next, as illustrated in FIG. 7(b), molten metal is loaded intothe first slurry vessel 2 a from the loading unit 4 and left in theelectromagnetic field for a predetermined time. As described above, theelectromagnetic field may be applied at the start or in the middle ofloading the molten metal into the first slurry vessel 2 a.

[0071] Next, as illustrated in FIG. 7(c), the piston 32 is moved down todraw the first slurry vessel 2 a out from the space 13. Next, asillustrated in FIG. 7(d), the piston 32 is rotated to switch the firstslurry vessel 2 a and the second slurry vessel 2 b, which is empty. Theslurry in the first slurry vessel 2 a is cooled at an appropriate rateto form a semi-solid metallic slurry containing a predetermined amountof solid. The piston 32 is raised again, as illustrated in FIG. 7(e), torepeat the above processes on the second slurry vessel 2 b. The firstslurry vessel 2 a containing the semi-solid metal is transferred by atransfer unit, such as a robot 6, for a subsequent forming process.

[0072] A large amount of semi-solid metallic slurry can be manufacturedcontinuously using an apparatus according to the present inventiondescribed above with more convenience when applied to a subsequentprocess and enhanced overall processing efficiency.

[0073] Laterally shifting a slurry vessel can be achieved in variousother ways, in addition to the method described in the above embodiment.For example, the driving unit 3 may be constructed to be laterallymovable along a rail 36, as shown in FIG. 8.

[0074] The methods and apparatuses for manufacturing a semi-solidmetallic slurry according to the present invention are compatible withvarious kinds of metals and alloys, for example, aluminum, magnesium,zinc, copper, iron, and alloys of the forgoing metals, for rheocasting.

[0075] Semi-solid metallic slurries manufactured according to thepresent invention contain micro spherical particles of even distributionwith an average diameter of 10-60 μm and provide improved mechanicalproperties, even for alloys. According to the present invention, suchuniform spherical particles can be formed within a short time throughelectromagnetic stirring initiated at a temperature above the liquidustemperature of a source metal to generate more nuclei throughout theslurry vessel.

[0076] When using a semi-solid metallic slurry manufacturing apparatusaccording to the present invention, the overall slurry manufacturingprocess can be simplified, and the duration of electromagnetic stirringand forming (casting) time can be greatly shortened, thereby savingenergy for the stirring and costs. The semi-solid metallic slurrymanufacturing apparatus according to the present invention makes itconvenient to perform a subsequent process and increases the yield offormed products.

[0077] While the present invention has been particularly shown anddescribed with reference to exemplary embodiments thereof, it will beunderstood by those of ordinary skill in the art that various changes inform and details may be made therein without departing from the spiritand scope of the present invention as defined by the following claims.

What is claimed is:
 1. A method of manufacturing a semi-solid metallicslurry, the method comprising: applying an electromagnetic field to aspace containing a slurry vessel; loading a molten metal into the slurryvessel in a state where the electromagnetic field is applied to thespace; and drawing the slurry vessel out from the space.
 2. The methodof claim 1, wherein applying the electromagnetic field to the space isperformed prior to loading the molten metal into the slurry vessel. 3.The method of claim 2, wherein applying the electromagnetic field to thespace is performed prior to placing the slurry vessel in the space. 4.The method of claim 1, wherein applying the electromagnetic field to thespace is performed at the start of loading the molten metal into theslurry vessel.
 5. The method of claim 1, wherein applying theelectromagnetic field to the space is performed in the middle of loadingthe molten metal into the slurry vessel.
 6. The method of claim 1,wherein applying the electromagnetic field to the space is sustaineduntil a slurry in the slurry vessel has a solid fraction in the range of0.001-0.7.
 7. The method of claim 6, wherein applying theelectromagnetic field to the space is sustained until the slurry in theslurry vessel has a solid fraction in the range of 0.001-0.4.
 8. Themethod of claim 7, wherein applying the electromagnetic field to thespace is sustained until the slurry in the slurry vessel has a solidfraction in the range of 0.001-0.1.
 9. The method of claim 1, furthercomprising cooling the slurry vessel containing the molten metal afterloading the molten metal into the slurry vessel.
 10. The method of claim9, wherein cooling the slurry vessel containing the molten metal issustained until a slurry in the slurry vessel has a solid fraction inthe range of 0.1-0.7.
 11. The method of claim 9, wherein cooling theslurry vessel containing the molten metal is performed at a rate ofapproximately 0.2-5.0° C./sec.
 12. The method of claim 11, whereincooling the slurry vessel containing the molten metal is performed at arate of approximately 0.2-2.0° C./sec.
 13. An apparatus formanufacturing a semi-solid metallic slurry, the apparatus comprising: atleast one slurry vessel; at least one stirring unit having a space forthe at least one slurry vessel and applying an electromagnetic field tothe space; a driving unit moving the slurry vessel at least up and downto place the slurry vessel in the space; and a loading unit loading amolten metal in liquid state into the slurry vessel.
 14. The apparatusof claim 13, wherein the at least one stirring unit applies theelectromagnetic field to the space prior to loading the molten metalinto the at least one slurry vessel.
 15. The apparatus of claim 13,wherein the at least one stirring unit applies the electromagnetic fieldto the space at the start of loading the molten metal into the at leastone slurry vessel.
 16. The apparatus of claim 13, wherein the at leastone stirring unit applies the electromagnetic field to the space in themiddle of loading the molten metal into the at least one slurry vessel.17. The apparatus of claim 13, wherein the driving unit moves the slurryvessel up after a predetermined time from loading the molten metal intothe at least one slurry vessel to draw the at least one slurry vesselout from the space.
 18. The apparatus of claim 13, wherein the drivingunit laterally shifts the at least one slurry vessel.
 19. The apparatusof claim 18, wherein the driving unit comprises a rotary platesupporting the at least one slurry vessel at an edge, moving the atleast one slurry vessel down after a predetermined time from loading themolten metal into the at least one slurry vessel, and rotating therotary plate to draw the at least one slurry vessel out from the space.20. The apparatus of claim 18, wherein the driving unit is laterallymoveable along a rail, moves the at least one slurry vessel down after apredetermined time from loading the molten metal into the at least oneslurry vessel, and is moved along the rail to draw the at least oneslurry vessel out from the space.
 21. The apparatus of claim 13, whereinthe at least one stirring unit applies the electromagnetic field to thespace until a slurry in the at least one slurry vessel has a solidfraction in the range of 0.001-0.7.
 22. The apparatus of claim 21,wherein the at least one stirring unit applies the electromagnetic fieldto the space until the slurry in the at least one slurry vessel has asolid fraction in the range of 0.001-0.4.
 23. The apparatus of claim 22,wherein at least one stirring unit applies the electromagnetic field tothe space until the slurry in the at least one slurry vessel has a solidfraction in the range of 0.001-0.1.
 24. The apparatus of claim 13,wherein the at least one slurry vessel includes a temperature controlelement.
 25. The apparatus of claim 24, wherein the temperature controlelement comprises at least one of a cooler installed in the at least oneslurry vessel and an external electric heater.
 26. The apparatus ofclaim 24, wherein the temperature control element cools a slurry in theat least one slurry vessel to reach a solid fraction of approximately0.1-0.7.
 27. The apparatus of claim 24, wherein the temperature controlelement cools the slurry in the at least one slurry vessel at a rate ofapproximately 0.2-5.0° C./sec.
 28. The apparatus of claim 27, whereinthe temperature control element controls the slurry in the at least oneslurry vessel at a rate of approximately 0.2-2.0° C./sec.